A driver assistance system is nowadays often part of the standard equipment of a modern motor vehicle. The purpose of such a driver assistance system is to increase highway safety by taking precautions to avoid hazard situations that could lead to accidents. Further aims are to increase comfort by unburdening the driver and to facilitate orientation by providing information on the surroundings that is situation-dependent and makes sense to the driver.
A driver assistance system can intervene semi-autonomously or autonomously in the propulsion, control or signaling devices of the vehicle, warn the driver shortly before or during a critical situation or prevent the latter by independent intervention. Here a driver assistance system is designed so that the responsibility rests with the driver and the latter can therefore override autonomous interventions.
Here a brake assist system, or “brake assistant” for short, is particularly important. In hazard situations, in which emergency braking is necessary, to avoid a collision, the brake pedal is often depressed with excessive hesitancy. In this case the brake assistant ensures maximum brake servo pressure and thus generally the minimum braking distance.
Emergency brake assist (EBA), by way of example, detects critical traffic situations and ensures optimum braking. To this end the entire area ahead of the vehicle itself is continuously monitored by means of a suitable sensor for distance and speed measurement, such as for example radar, LIDAR (Light Detection And Ranging) or a camera. In this way, other vehicles that are either stationary or moving, or general obstructions on the highway, are captured. If the distance between the vehicle itself and a vehicle travelling ahead of it falls below a level that at the current vehicle speed is deemed critical, the driver is alerted and/or the brake system performs a slight pre-braking, to reduce the braking distance. If the driver then moves their foot from the gas pedal to the brake, the brake assistant simultaneously increases the braking force. If the driver then actively contributes to the braking maneuver, the system provides the necessary braking force to prevent a collision with the vehicle travelling ahead or with other highway users.
If a driver encounters a situation in which, by way of example due to inattentiveness or an unexpected obstruction, they can no longer brake independently and if a collision with an unexpected obstruction is imminent, by means of an autonomous full braking function (autonomous emergency braking—AES) a braking assistant can initiate a fully automatic emergency braking. In this way, the accident can either be completely avoided or at least the seriousness of it lessened.
However, such a full braking function becomes particularly problematic if the direction of travel of the vehicle itself (ego-vehicle or subject vehicle) is unknown. If another vehicle ahead of the ego-vehicle is reversing, then to avoid a collision it is also necessary for the ego-vehicle to reverse. But if the reversing or backward-rolling vehicle ahead is moving faster than the ego-vehicle itself is moving, then the distance between the vehicles lessens and in the worst case falls below the specified critical minimum distance value. In this case a braking assistant, having no knowledge of the direction of travel, commences a braking maneuver, whereby the distance between the two vehicles undesirably reduces further. In such a situation, a collision is almost unavoidable.